This invention relates to a fluid displacement apparatus, and more particularly, to a scroll type fluid displacement apparatus for use as a supercharger for an engine or as an air pump.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801, 182 (Creux) discloses a device including two scrolls, each having a circular end plate and a spiroidal or involute spiral element. These scrolls are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases of decreases dependent on the direction of the orbital motion, the scroll type fluid apparatus is applicable to compress, expand or pump fluids.
Scroll type displacement apparatus have been used as refrigeration compressors in refrigerators or air conditioning apparatus. Such compressors need high efficiency and a high compression ratio, such as a 5 to 10 compression ratio. In such a compressor, the re-expansion volume, i.e., the smallest volume of the fluid pockets in the compression cycle, which is located at the center of the scroll members in a scroll type compressor, must be reduced as much as possible. To this end, the inner end portions of the spiral elements are extended inwardly as far as possible to the center of the scroll member.
The conventional driving mechanism in a high compression ratio scroll type compressor is connected to the end plate of an orbiting scroll on a side opposite the spiral element. The acting point of the driving force of the driving mechanism on the orbiting scroll generally is displaced from the acting point of the reaction force of the compressed gas, which acts at an intermediate location along the height of the spiral element of the orbiting scroll. If the distance between these acting points is relatively long, a moment is created which adversely effects the stability of the orbiting scroll during orbital motion. Therefore, to compensate for this loss of stability, the length of the spiral element generally is limited, which in turn limits the volume of the apparatus.
The above limitation on the length of the spiral element is not a problem for a scroll type fluid displacement apparatus which requires a compression ratio of only 1.0 to 1.5, since the re-expansion volume need not be reduced as much as in a high compression ratio apparatus. In apparatus which requires only a low compression ratio, the difference between the high pressure space and the lower pressure space is smaller than in a high compression ratio apparatus, so that 1.5 to 2.0 revolutions of the spiral element generally is sufficient.
A scroll type fluid displacement apparatus having a driving mechanism for reducing pressure loss, which is needed to obtain high flow rates, is disclosed in copending application Ser. No. 354,512, filed on March 3, 1982. Although the driving mechanism in this application improves the stability of orbital motion of the orbiting scroll without interference with the flow of fluid in the center portion of the spiral elements, the driving crank must be durable to endure the centrifugal force of the orbiting scroll and to avoid bending at high rotation speeds. Generally, the driving mechanism disclosed in this copending application may not be entirely suitable for high rotation speeds.